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DAC costs depend on the weather

In principle. direct air capture (DAC) can be placed anywhere in the world. For carbon storage, ideally a DAC plant is placed near inexpensive storage capacity, for example near a depleted oil well in Louisiana, or near a basalt rock formation in a location such as Iceland. However, Louisiana and Iceland have significantly different climates, and the ambient temperature and humidity make a difference in performance. How much of a difference?

In October, researchers at Imperial College in London presented a paper that analyzes the impact of regional climate variation on the cost of DAC for solid sorbent systems. Results show that lower humidity (around 20-60%) and low ambient temperatures improve electricity requirements and productivity, because regeneration energy and sorbent capacity are not wasted on absorbing and desorbing water. If the temperature goes too low - for example, -15°C - this causes problems. Overall, Alaska is thus not a very good location for DAC (it's too cold), but Iceland is fine (and better than Louisiana). The electricity requirements are unsurprisingly lowest in the desert southwest of the US, or the Middle East.

The authors also did a full cost analysis based on regional climate, and the differences are substantial. The US mountain west has some of the best conditions in the world, with both low temperatures and humidity, and proximity to storage sites. There is ample reason to expect Wyoming, for example, to become a DAC hub for sorbent-based capture processes.

A second paper, published at the same conference, looked at the climate impact on DAC using water-based liquid processes like that used by Carbon Engineering. Unsurprisingly, humidity was not a huge factor here - the evaporation of water is higher in dry environments, and that imposes some cost, but mot much. Temperature, by contrast, had a huge impact, as the kinetics of transfer of CO2 from air to liquid are much better at higher temperature. Raising the ambient temperature from 10°C to 30°C might reasonably cut the cost of capture by 20%. This is a huge effect, and implies that the Carbon Engineering process will operate most efficiently in warmer areas, like south Texas or the Middle East. Wyoming and Canada need not apply.

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